An ultrasonic nebulizing apparatus and system including a pzt crystal, supported in a container adapted to support a nebulization cup at a position spaced from the transducer; the container also adapted to contain a fluid coupling column. An oscillator, when energized causes the crystal to oscillate...http://www.google.com/patents/US3828773?utm_source=gb-gplus-sharePatent US3828773 - Nebulizing apparatus and system

An ultrasonic nebulizing apparatus and system including a pzt crystal, supported in a container adapted to support a nebulization cup at a position spaced from the transducer; the container also adapted to contain a fluid coupling column. An oscillator, when energized causes the crystal to oscillate at its ultrasonic mechanical resonant frequency, the oscillator being designed to oscillate at a frequency governed by the mechanical resonant frequency of the crystal. The system includes a safety circuit associated with the oscillator and including the container, the cup and the coupling column, which is effective to deenergize the system in the absence of operational conditions within the system.

NEBULIIZING APPARATUS AND SYSTEM BACKGROUND OF THE INVENTION Nebulizers are well known devices having many applications. Inhalation therapy, a well known technique of medical treatment, is one such application.

One type of nebulizer is an ultrasonic nebulizer. In this type of device, ultrasonic energy is utilized to nebulize a liquid or solution. The nebulized solution is carried by a dynamic air flow passed through the nubulized solution into the atmosphere in the vicinity of a patient, or directly to the patient.

Such nebulizers find their primary use in medical institutions, such as hospitals, and will be used primarily by medically trained personnel rather than by a technically trained staff. It is important, therefore, that such nebulizing apparatus be simple to operate, present minimal safety hazards in operation, and be easily maintained.

Basically, an ultrasonic nebulizer incorporates a crystal which is driven by an electronic drive circuit or oscillator at an ultrasonic resonant frequency. The crystal mechanically oscillates at this resonant frequency and transmits ultrasonic energy through a fluid coupling column, typically water, to a solution to be nebulized within a container or cup maintained in contact with the fluid coupling column.

The utilization of ultrasonic type nebulizers has not achieved full potential because of a number of deficiencies found in existing units. As explained above, the crystal for generating the ultrasonic energy used for nebulizing the solution is driven electronically by an electronic drive circuit or oscillator. Such crystals exhibit high characteristics, i.e., the frequency of the drive circuit must correspond quite closely to the me chanical resonant frequency of the crystal, or to harmonies or sub-harmonics thereof, in order to properly drive the crystal and cause it to mechanically oscillate. While crystals to be used in anultrasonic nebulizer may be selected to have the same nominal resonant frequency, the actual resonant frequency of each crystal may vary. Existing oscillator or electronic drive circuits either require tuning to the actual resonant frequency of the crystal each time that the oscillator is utilized with a different crystal or incorporate complex circuitry. Since the operating personnel of such nebulizers are generally not technically trained, the need to continually retune the oscillator detracts from its ease of operation, and the complex circuitry associated with any automatic tuning circuits adversely affects reliability, all necessary when electronic systems are employed in medical institutions and are utilized by non-technical personnel.

Another deficiency in such devices is inadequate safety, particularly with respect to potential damage to the device itself and possible injury to personnel. As explained above, the crystal is fluid coupled to the solution that is being nebulized. It is necessary to maintain the fluid coupling between the crystal and thesolution, since the absence of such coupling not only terminates the nebulization of the solution, but removes the load on the crystal. Under these circumstances, the crystal rapidly heats up and is destroyed, necessitating replacement of the crystal, and, in existing devices, the retuni ng of the electronic drive circuit to the resonant frequency of the new'crystal.

Personnel safety is, of course, a concern. When the crystal is being driven, and the fluid coupling is accessible, ultrasonic burn can occur if, for example, a finger is brought into contact with energized fluid coupling. In existing devices, this can occur when the nebulizer cup is removed from the open end of the coupling container, thereby providing access to the fluid coupling.

In addition to equipment and personnel safety deficiencies, existing nebulizer configurations have not provided the desired efficient transfer of the nebulized solution to the dynamic air stream. This inefficiency is, at least in part, a result of the configuration of the nebulizing cup. These inefficiencies can occur because of improper coupling between the cup and the fluid coupling column, thereby resulting in improper and unsatisfactory nebulization of the solution itself, or from inefficient transfer of the nebulized solution to the air stream.

In order to obtain efficient transfer, the dynamic air flow should make contact with the main portion of the nebulized solution-the fountain-so that the very small nebulized particles, are picked up by the air flowing through the nebulizing cup. The efficient transfer of the nebulized solution to the dynamic air flow permits supersaturation of the air with the nebulized solution at desired flow rates.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided an ultrasonic nebulizing apparatus and system of increased efficiency, which incorporates electronic drive circuitry which does not require constant retuning, i.e., which tunes itself to the resonant frequency of the crystal, and in which the crystal is deenergized in the absence of fluid coupling between the crystal and the nebulizer cup in order to preclude and inhibit damage to the crystal itself and to prevent personnel injury.

The nebulizing system of the present invention incorporates a disposable solution containing cup for ultrasonic nebulizers which is designed to promote efficient transfer of the nebulized solution to the dynamic gas stream, e.g., air, oxygen, other suitable gases, or mixtures thereof, to promote a desired spray mist, and which insures proper coupling between the solution within the cup and the fluid coupling column when the cup is in place in the nebulizer.

The nebulizing system of the present invention is designed to be deenergized in the absence of proper operating conditions, e.g., in the absence of fluid coupling between the crystal and the cup, or in the absence of the cup itself, in order to prevent damage to the crystal and to preclude injury, such as ultrasonic burn, when the fluid coupling column becomes accessible.

With these safety features and efficient transfer of the nebulized solution, the nebulizing system of the present invention may be adapted for numerous uses. For example, an in-line heater can be incorporated in the gas outlet of the nebulizer to provide temperature control of the fine spray. This temperature control may be desirable to raise the temperature of the spray to body temperature, to increase the moisture carrying capability of the gas, to convert the nebulizing system into a humidifier or for any other reason that it may be desirable to control the gas temperature.

In accordance with the safety considerations incor porated into the present invention, the in-line heater may be temperature sensitive to prevent overheating, and may be also deenergized by the nebulizer safety circuit.

The nebulizing apparatus and system of the present invention is suitable for use with standard Intermittent Positive Pressure Breathing (IPPB) devices or with standard anesthesia circuits.

Furthermore, the design of the nebulizing cup of the present invention renders the nebulizing apparatus and system particularly suitable for controlled single or multiple dosage, or for continuous dosage. The dosage can be readily controlled by observation and standard I/V systems available in many medical institutions can be utilized.

More specifically, the nebulizing apparatus and system of the present invention comprises the fluid coupling and crystal holding container, a self-tuning oscillator for driving the crystal and a nebulizing cup which contains the solution to be nebulized. A disposable nebulizing cup for ultrasonic oscillators is the subject of divisional co-pending U.S. Pat/application Ser. No. 29l,293, entitled Nebulizing Cup for Ultrasonic Nebulizing System, filed concurrently with this application.

The oscillator for driving the crystal or transducer is designed to oscillate at the driving frequencythe mechanical resonant frequency of the crystal, or more often, a sub-harmonic thereof. Typically, the driving frequency equals one-half the mechanical resonant frequency of the crystal. In accordance with the present invention the oscillator circuit is operated to generate the proper driving frequency for crystals whose actual resonant frequency may vary from the nominal resonant frequency, for example, by as much as i percent.

In addition to generating an output consisting of the driving frequency, the system of the present invention also includes a safety control circuit. The safety control circuit is energized when the system is operational, i.e., when the system is energized and when there is sufficient fluid in the coupling column and when the nebulizing cup is in place. When operational conditions do not exist, for example, in the absence of the nebulizing cup, or when there is insufficient fluid in the coupling column to provide adequate coupling between the crystal and the cup, the safety control circuit is deener gized. The deenergization of the safety control circuit effects deenergization of the oscillator drive circuit, and may also be effective, if desired, to deenergize the fan which propels the dynamic air flow through the nebulizer cup as well as any other electrical components incorporated into the system such as an in-line heater.

As a result, the nebulizing apparatus and system becomes deenergized in response to the non-existance of operational conditions, particularly those which might result in damage to the equipment or in injury to personnel.

The self-tuning capabilities of the oscillator drive circuit simplifies operation of the system by eliminating the necessity for operating personnel to retune the oscillator each time it is used with a different crystal or in the event that the resonant frequency of the crystal drifts with age. This eliminates the necessity for continuously monitoring the apparatus and system to insure proper operation and permits it to operate efficiently for extended periods of time, e.g., when continuous dosage is desired.

Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and of one embodiment thereof, from the claims and from the accompanying drawings in which each and every detail shown is fully and completely disclosed as a part of this specification, in which like numerals refer to like parts.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS FIG. 1 is a block diagram of an ultrasonic nebulizing system in accordance with the present invention;

FIG. 2 is a schematic circuit diagram of one embodiment of the present invention;

FIG. 3 (with FIG. 1) is a perspective view with portions broken away of the physical components forming part of the nebulizing system of the present invention;

FIG. 4 is a side view, partially in section, of the components shown in FIG. 3;

FIG. 5 is a partially enlarged sectional view similar to FIG. 3;

FIG. 6 (with FIG. 1) is a top view of a disposable cup; and

FIG. 7 is a perspective view of a cup contact.

DETAILED DESCRIPTION While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail one specific embodiment, with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated.

The system of the present invention is disclosed diagrammatically in FIG. 1 wherein a pzt crystal 10 is driven by an oscillator 12. The oscillator 12 is connected to a power supply 14 through first normally open contacts of a safety control switch 16. The output of oscillator 12 is an ac. signal which typically is a subharmonic of the ultrasonic mechanical resonant frequency of crystal 10.

A safety control circuit is operative in the absence of operational conditions, e.g., the lack of sufficient amount of fluid in the fluid coupling column in the coupling chamber or in the absence of a cup in the coupling container to effectively turn off the oscillator 12, as well as other components in the system. The safety control circuit includes a safety sensing circuit 18 connected in parallel with crystal 10. The safety sensing circuit 18 is connected to the switched input of a switched safety control amplifier 20, which is normally energized when the system is operational.

Power supply 14 is also connected to a fan 22 and to other electrical components, such as in-line heater 24, through other normally open contacts of safety control switch 16. The output of switched safety control amplifier 20 is connected to an alarm indicator 26 through normally closed contacts of safety control switch 16.

In operation, when the system is energized, the safety sensing circuit 18 is responsive to the presence of operational conditions, e.g., the presence of the cup and sufficient fluid in the coupling column to energize the switched safety control amplifier 20, thereby closing the normally open contacts of safety control switch 16, to energize oscillator 12, fan 22, heater 24 and any other electrical components, and open the normally closed contacts connected to the alarm indicator 26. The safety sensing circuit 18 is responsive to the absence of these operational conditions, the absence of the nebulizer cup, or an insufficient amount of fluid in the coupling column to provide coupling between the crystal and the nebulizer cup, to deenergize the safety control switched amplifier 20. When the switched amplifier 20 is deenergized, the contacts of the safety control switch 16 return to their normal" position to deenergize oscillator 12, fan 22 and in-line heater 24, and to actuate alarm indicator 26. As a result, damage to the crystal 10 is prevented, potential injury to operating personnel is obviated and the system is deenegized until the reasons which-caused actuation of the safety circuit have been corrected.

FIG. 2 is a schematic diagram of the system of FIG. 1. A transformer 28 includes a primary winding 30 connected through a fuse 32 and power switch 34 to a source of ac. potential. A power on indicator light 36 is connected across the primary 30 and is energized when power switch 34 is closed.

The transformer 28 has two secondary windings 38, 40. A full wave bridge rectifier 42 is connected across the entire secondary winding 38, or across a portion thereof through tap 43, by a high-low selector switch 44. A filter circuit including choke 46 and capacitors 48, 50 and 52 is connected across the output of rectifier 42 between line 54(B-) and ground 56. Line 54 is connected to the input of the oscillator 12 through the normally open contacts 581 of a safety control relay 58 (corresponding in function to safety control switch 16 of FIG. 1).

Line 54( B-), is connected to one end of input resistor 60 which forms part of a voltage divider with bias resistor 62 the other end which is connected to ground 56. A bypass capacitor 63 is connected across bias resistor 62. The junction of resistors 60, 62 is connected to the base 64 of transistor 66 through a tuned parallel tank circuit 68 consisting of inductor 70 and capacitor 72. The collector 74 of transistor 66 is connected to ground 56, while the emitter 76 of transistor 66 is connected to line 54(B-) through a choke coil 78. The emitter 76 is also connected through coupling capacitor 80 and'the single wire 82 of a shielded cable 84 (See FIG. 3) to one side of crystal 10 the other side of which is connected to the grounded shield 86 of the cable 84.

The safety sensing circuit 18 includes series connected coil 88 and a capacitor 90 which are connected across crystal 10. The water coupling column 92 is connected across capacitor 90 through contacts 94, 96.

Power for the switched amplifier 20, for the fan 22 and for other components such as in-line heater 24, is taken off the secondary 40 of transformer 28. A full wave bridge rectifier 98 is connected across the output of rectifier 98 between line l02(B and ground 104.

Fan 22, including fan motor 22a and rheostat 22b, and in-line heater 24 are connected between line 102 and ground 104 through the normally open contacts 58-2 of safety control relay 58. The alarm indicator 26 is connected between line 102 and ground 104 through the normally closed contacts 58-3 of the safety control relay 58.

The switched amplifier 20 is a relatively standard Darlington configuration consisting of transistors 106 and 108, load resistor 110 in the emitter circuit of transistor 106, resistor 111 in the collector circuit of transistor 106, capacitors 112, 114, and an input voltage divider connected to the base of transistor 106. The

input voltage divider includes resistors 116, 118 and is developed across resistors 116, 118, the resistance of fluid coupling column 92 and the crystal 10. The relative values of resistors 116, 118 are selected in conjunction with the resistance of fluid coupling column 92 and crystal 10 so that when the system is operational, i.e., when the cup is in place and when there is sufficient fluid in the coupling column, transistor 106 conducts and the switched amplifier 20 is energized. When the switched amplifier 20 is energized, current passes through relay coil 58, connected in the collector circuit of transistor 108 and the normally open relay contacts 58-1, 58-2 are closed, while the normally closed relay contacts 58-3 are opened.

When the bypass fluid column circuit is opened, a dc. voltage is developed across capacitor 90, which in connection with voltage divider resistors 116, 118 deenergizes switched amplifier 20 to release or deactuate relay 58. When relay 58 is deactuated, the normally open contacts 58-1 and 58-2 return to their normal position (as shown in FIG. 2) to deenergize oscillator 12, and, therefore, crystal 10, as well as fan 22 and in-line heater 24. At the same time, normally closed contacts 583 return to their normal position (as shown in FIG. 2) to energize alarm indicator 26.

One physical embodiment of the nebulizing apparatus and the nebulizing cup is shown in FIGS. 3-6. Crystal 10 is supported in the bottom 124 of a generally cylindrical coupling container 125 having a first cylindrical side wall 126 extending up from bottom 124 to define a coupling chamber 127 for the fluid coupling column 92. The crystal 10 is supported in a crystal holder 128, best shown in FIG. 5.

The crystal holder 128 includes a first electrically conductive, open ended, cylindrical housing 130 which extends into coupling chamber 127 through the bottom 124, to which the housing 130 is suitably bonded or otherwise affixed. The cylindrical housing 130 terminates at its upper end within the coupling chamber 127 in an inwardly extending retaining lip 132. The crystal 10, which has on its upper, concave surface a conductive layer 134 that covers the entire upper concave surface of the crystal and extends around the periphery thereof, is disposed within the housing 130 with the conductively coated periphery in electrical contact with the housing. An 0 ring 136 provides a water tight seal between the crystal 10 and the retaining lip 132. The crystal 10 is held in place by a conductive retaining ring 138 threaded internally of housing 130 up against the periphery of crystal 10 and the conductive coating 134 thereon. The conductive coating 134 acts as the contact 96 (shown in FIG. 2) to provide an electrical connection from water column 92, as well as crystal 10, to ground.

An additional conductive coating 140 on the lower convex surface of crystal is spaced away from, or otherwise electrically insulated from, conductive coating 134. A spring like electrode 142, supported on insulated disc 144 is brought into contact with conductive coating 140 and held in place by conductive collar 146 threaded internally of housing 130. Conductive collar 146 is connected to ground through the shield 86 of cable 84, while electrode 142 is connected to the single wire 82 of cable 84. Although the disclosed embodiment of the crystal holder 128 has distinct advantages, e.g., it permits easy replacement of crystal when necessary, alternative approaches for mounting the crystal may be used.

The cylindrical coupling container 125 includes, in addition to bottom 124 and side 126, which define the coupling chamber 127 for water column 92, an upper cylindrical side wall 150 having a greater diameter than the diameter of the side wall 126 and connected thereto by an integral lateral shoulder 152. Shoulder 152 is adapted to support a nebulizer cup 154 thereon with the upper side wall 150 retaining the cup 154 in position. A conductive contact 156 is disposed on the upper surface of annular shoulder 152 and is electrically connected to a conductor 158 formed in cylindrical wall 126 and extending from contact 156 through the bottom 124 of the coupling container 125. Conductor 158 is connected to the wire 82 through safety choke coil 88, and is also connected to grounded cable shield 86 through safety capacitor 90.

Since the water coupling column 92 should not directly touch contact 156, one or more overflow apertures 159 may be provided in cylindrical wall 126 below shoulder 152 to provide a spillover for excess water in coupling chamber 127 when the cup 154 is placed in the container 125.

The nebulizing apparatus and system of the present invention is particularly adapted for use with a disposable, sterile, nebulizing cup. One such cup is the subject of co-pending divisional US. Pat. application Ser. No. 291,293 and is shown in FIGS. 3, 4, and 6.

Functionally, the cup 154 may be considered to incorporate a solution containing chamber 160 and a nebulizing or fountain chamber 162. When inserted into the container 125, the solution chamber 160 of cup 154 should be disposed at and below the focal point of crystal 10.

As shown in FIGS. 3 and 4, the solution chamber 160 is physically divided into a generally cylindrical or slightly tapered support section 164 and a coupling section 166 depending therefrom and adapted to enter the fluid column 92. A plurality of circumferentially spaced, axially extending ribs 168 are formed on the outer surface of the cylindrical wall 170 of support section 164. The ribs 168 engage the inner surface of upper cylindrical wall 150 to properly position and stabilize the cup 154 when inserted into the container 125.

The side wall 172 of coupling section 166 is tapered inwardly from a point offset from the periphery of support section 164 to define a support shoulder 174 adapted to seat on shoulder 152 of container 125 when the cup 154 is inserted into the container. The side wall 172 of coupling section 166 depends from the open bottom of support section 164 and tapers inwardly to a generally curvilinear bottom portion 172 which is effectively a continuation of side wall 172. The configuration of the side wall 172 and the bottom portion 172 of coupling section 166 is selected to eliminate any flat surface at the bottom of the coupling section which might, when the cup 154 is inserted into the container and the coupling section 166 enters the fluid coupling column 92, entrap air bubbles against such a flat bottom surface. The existence of such entrapped air bubbles diminishes the coupling between the water column 92 and the coupling section 166 and produces improper and inadequate nebulization of the solution contained within a solution chamber 160.

A fountain chamber 162 of cup 154 rises above support section 164 and may conveniently be of a greater diameter. The height of fountain chamber 162 is selected to permit formation of the nebulization fountain with minimum interference. The fountain chamber 162 has a generally curvilinear top 176 formed integrally therewith having its maximum height along the vertical axis of the cup. A recess 178 may be formed in the top 176 and is designed to accommodate a standard l/V needle system (not shown). The recess itself is adapted to receive and retain the shank of the l/V needle with the needle penetrating the bottom wall 180 of the recess 178. An l/V system may be utilized when it is desired to maintain the level of the solution being nebulized, for example, when the nebulizer is being used for continuous treatment.

The fan 22 is located upstream of the cup and forces gas through an inlet 182 formed in the generally cylindrical side wall 186 of the nebulization chamber 162. The gas is driven through inlet 182 through the nebulizing chamber 162 and out of a gas outlet 188 also formed in the cylindrical side wall 186. The relative positions of the inlet 182 and the outlet 188 with respect to each other are selected to cause the gas flowing through nebulizing chamber 162 to interact with the nebulization fountain rising along the vertical axis of the cap 154 to effect efficient transfer of the nebulized solution to the dynamic gas flow.

FIG. 7 shows one embodiment of contact 94 (shown schematically in FIG. 2) for completing the safety circuit through water column 92. The contact 94, as shown in FIG. 7 is a foil ring 190 having a pair of bendable fingers 192 extending across the diameter of the foil ring 190. The foil ring 190 is adapted to be inserted over coupling section 166 and is adhered to the support shoulder 174 of support section 164. When the foil ring 190 is inserted over coupling section 166, the fingers 192 are forced down along the sides of coupling section 166. As seen in FIG. 4, when the cup 154 is inserted into the container 125 the contact fingers 192 make electrical contact with the water coupling column 92 to complete the safety circuit to grounded shield 86 through the cylindrical housing 130 and the conductive collar 146.

In the cup shown in the drawing, the gas inlet 182 and the gas outlet 188 are shown of finite, limited length. it should be apparent that the length of the inlet 182 and the outlet 188 can be of any desired length and may be formed with a sealed membrane at the termination thereof to effectively provide a sterile cup prior to use. The in-line heater 24 is inserted downstream of the outlet 192 in any suitable fashion.

In one embodiment of the present invention, in which the nominal resonant mechanical frequency of the crystal 10 is 2 mhz, and the oscillator is designed to operate about a center frequency of l mhz, the following components were utilized and their values were as follows:

Gen. Elec. D33D22 Gen Elec. D4OD4 transistor 106 transistor 108 From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the true spirit and scope of the novel concept of the invention. it is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.

We claim:

1. An ultrasonic nebulizing system comprising: an ultrasonic transducer having an ultrasonic resonant mechanical frequency; a nebulizing cup adapted to contain a solution to be nebulized;

a container supporting said transducer and said cup in spaced apart relation to said transducer;

a fluid column within said container for coupling the ultrasonic energy generated by said transducer to said cup supported by said container, the absence of fluid coupling between said transducer and said cup supported by said container defining an absence of operational conditions within said system;

electric drive circuit means electrically connected to said transducer, said drive circuit means when energized generating an ac. signal causing said transducer to oscillate at its mechanical resonant frequency; and

safety circuit means operatively associated with said drive circuit means for deenergizing said drive circuit means and said transducer in response to the absence of operational conditions within said system.

2. A system as claimed in claim 1 including means for energizing said safety circuit means in response to the existence of operational conditions within said system to effect energization of said drive circuit means, and for deenergizing said safety circuit means in response to the absence of said operational conditions within said system to effect said deenergization of said drive circuit means.

3. A system as claimed in claim 2 wherein one of said operational conditions is the existence of fluid coupling between said transducer and said cup supported by said container,

said means for energizing and deenergizing said safety circuit means including sensing circuit means including said fluid coupling column responsive to the presence of said fluid coupling to energize said safety circuit means and responsive to the lack of said fluid coupling to deenergize said safety circuit means.

4. A system as claimed in claim 3 wherein said sensing circuit means incorporates a dc. circuit path through said fluid coupling column,

said sensing circuit means operative to deenergize said safety circuit means in response to the opening of said d.c. circuit path.

5. A system as claimed in claim 4 wherein said d.c. circuit path includes first contact means disposed in proximity to said transducer and second contact means spaced from said transducer, and said fluid coupling column extending therebetween,

said d.cv circuit path opening when there is insufficient fluid in said coupling column to engage both said first and second means and alternatively upon movement of said second contact means out of engagement with said coupling column.

6. A system as claimed in claim 5, wherein said second contact means includes a fixed contact on said container spaced away from said coupling column and a removable contact on said cup supported by said container,

said removable contact engaging both said fixed contact and said coupling column when said cup is supported by said container to complete said do circuit path.

7. A system as claimed in claim 2 wherein one of said operational conditions is the presence of said cup supported by said container,

said means for energizing and deenergizing said safety circuit means including sensing circuit means including electrical contact means on said cup and said container electrically engaging when said cup is supported by said container, said sensing circuit means responsive to the absence of such electrical engagement between said contact means to deenergize said safety circuit means.

8. A system as claimed in claim 1 wherein said electric drive circuit comprises an oscillator circuit, wherein said transducer is connected to said oscillator circuit as a high Q load circuit, said oscillator circuit being designed to oscillate at a resonant frequency corresponding to the nominal mechanical resonant frequency of said transducer or at harmonics or subharmonics thereof, said oscillator circuit including circuit means effecting actual oscillation thereof at a resonant frequency corresponding to the actual mechanical resonant frequency of said transducer, or at harmonics or sub-harmonics thereof, which actual mechanical resonant frequency may differ from said nominal mechanical resonant frequency.

9. A system as claimed in claim 8 wherein said circuit means includes amplifying circuit means and tuned circuit means of the type exhibiting maximum impedance at resonance connected to said amplifying circuit means, the designed resonance of said tuned circuit means being equal to the nominal resonant frequency of said oscillator, a positive feedback circuit provided by the internal interelectrode capacitance of said amplifying means, whereby the actual resonant frequency of said oscillator is determined by the actual mechanical resonant frequency of said transducer.

10. In an ultrasonic nebulizing system,

a crystal supported by a container and adapted to mechanically oscillate at an ultrasonic resonant frequency in response to an a.c. drive signal having a frequency equal to said resonant frequency, to harmonics thereof or to subharmonics thereof,

a cup adapted to contain a solution to be nebulized supported by said container at a position spaced from said crystal,

said crystal being operatively coupled to said cup through a fluid coupling column,

an oscillator for generating said a.c. drive signal,

a power source,

normally open switch means connecting said power source to said oscillator,

means coupling said a.c. drive signal to said crystal,

safety control circuit means operative when energized to close said normally open switch means and effect energization of said oscillator,

biasing means connected between the input of said safety control circuit means and said power source and including safety circuit sensing means connected across said crystal,

said safety circuit sensing means incorporating a do circuit path including said fluid coupling column and contact means on said cup,

said biasing means producing a dc. bias voltage to energize said safety control circuit in response to said d.c. circuit path being closed.

11. In a system as claimed in claim 10, including additional electrical components connected to said source through said normally open switch means, whereby said additional components are energized in response to the energization of said safety control circuit means.

12. In a system as claimed in claim 10, including alarm indicating means, normally closed switch means connecting said alarm indicating means to said power source, said normally closed switch means opening in response to the energization of said safety control circuit means and closing in response to deenergization thereof to actuate said alarm indicating means.

13. In an ultrasonic nebulizing system, having a container, a cup supported in said container, an ultrasonic crystal and a fluid column within said container for coupling said crystal to said cup;

a crystal holder structure for supporting said crystal in a wall of said container comprising;

a generally hollow open ended electrically conductive housing extending through said wall and attached thereto, the interior of said housing having a cross-sectional configuration complementary to the peripheral configuration of said crystal,

the inner end of said housing, disposed within said container, formed with a retaining lip,

said crystal being disposed within said housing and adjacent to said retaining lip, with its inner surface exposed to said fluid coupling column,

means disposed between said lip and the peripheral portion of said crystal to provide a fluid seal therebetween,

a first electrically conductive electrode formed around the periphery of said crystal;

a removable electrically conductive retaining ring disposed within said housing against said first electrode and the outer peripheral edge of said crystal to retain said crystal in place,

a second electrode in electrical contact with the outer surface of the said crystal and spaced from said first electrode, and

a collar removably attached to said housing, for retaining said second electrode in electrical contact a with said crystal.

14. In the system of claim 13, wherein said housing, said retaining ring and said collar are all electrically conductive,

said first electrode including a first conductive coating on the inner surface of said crystal and extending to and around the periphery thereof into electrical contact with said housing and said retaining ring, and said second electrode including a second conductive coating on the outer surface of said crystal electrically insulated from said first conductive coating, and wherein said second electrode is supported by an electrically insulated disc in contact with said second conductive coating, said disc being retained in place between said retaining ring and said collar.

15. In a system as claimed in claim 14 including an oscillator having an output and a ground connection for driving said crystal at its resonant frequency, and

single wire shielded cable means, the single wire of which is connected to said electrode and to the output of said oscillator and the shield of which is connected to said collar and to the ground connection of said oscillator.

16. In a system as claimed in claim 15, including a safety sensing circuit connected across said crystal and including a contact on the cup electrically connectable to said housing through said fluid coupling column and engageable to make electrical contact with a contact on said container disposed out of contact with said fluid coupling column to complete a circuit from said grounded housing through said fluid column to said container contact.

17. In a system as claimed in claim 16, said safety sensing circuit further including a capacitor connected between said container contact and said grounded shield and a choke coil connected between said container contact and said single wire of said cable means, whereby the output of said oscillator is electrically blocked from said sensing circuit by said choke coil and said coupling column is exposed only to a dc. signal. k i